While you have simple directories for customization code in ConfigBox for Joomla and Wordpress, in Magento 2 it takes a Magento module to place this code in (Magento code architecture reasons).
To customize your ConfigBox for Magento installation, you use this module and install it in the /app/code location. The module name is Rovexo/ConfigboxCustomizations and there is a subdirectory for your custom assets (like images, stylesheets, javascript) and customization code (custom language files, controllers, models, views etc).
Module download:
After installed and enabled, you can place your customization code in these directories:
Customization dir (language files, controllers, models, views etc):
/app/code/Rovexo/ConfigboxCustomizations/view/customizations/
Custom assets dir (stylesheets, javascript, images, fonts etc):
/app/code/Rovexo/ConfigboxCustomizations/view/base/web/
These two filesystem locations are referred to throughout the documentation.